Process for regulating molecular weight of vinylindene polymers by using 3, 5-dimethylcyclohexen-2-one-1



1 them more easily processable.

United States Patent 3,265,676 PROCESS FOR REGULATING MOLECULAR WEIGHT 0F VINYLINDENE POLYMERS BY USING 3,5-DIMETHYLCYCLOHEXEN- 2-0NE-1 Richard E. Delacretaz and Speros P. Nemphos, Springfield, Mass., assignors to Monsanto Company, St. Louis, Mo., a corporation of Delaware N0 Drawing. Filed May 18, 1964, Ser. No. 368,370 4 Claims. (Cl. 260-85.5)

This application is a continuation-in-part of our c0- pending application Serial No. 136,995, filed September 11, 1961, now abandoned.

The invention relates to the polymerization of a free radical-polymerizable material including a polar monomer and more particularly relates to a method of regulating the molecular weights of polymers prepared by polymerizing such a free radical-polymerizable material in the absence of an organic diluent.

The tendency of certain free radical-polymerizable materials to polymerize to very high molecular weight polymers under normal polymerization conditions is already Well known. These very high molecular weight polymers have the disadvantage of being difiicultly processable, i.e., unable to be processed without the use of special processing equipment except at temperatures so high as to have a detrimental ellect on the strength and color of the processed polymers.

Various techniques have been proposed for regulating the molecular weights of such polymers so as to make One of these techniques is to conduct the polymerization in an organic diluent. This technique is effective as a means of lowering molecular weight, but it has the disadvantages of increased cost and inconvenience of separating the polymer from the organic diluent. Other proposed techniques avoid the disadvantages of solvent polymerization but have unfortunate disadvantages of their own, e.g., raising the polymerization temperature increases the danger of a runaway polymerization, and using a mercaptan as a chain transfer agent contributes a very unpleasant odor to the polymers.

An object of the invention is to provide more easily processed polymers of the type prepared by polymerizing a free radical-polymerizable material including a polar monomer.

Another object is to provide a novel process for regulating the molecular weights of such polymers without employing an organic diluent in the polymerization reaction mixture.

These and other objects are attained by conducting the polymerization of a free radical-polymerizable material including a polar monomer, as hereinafter more completely described, in the presence of 0.05-5% of 3,5- dimethylcy-clohexen-Z-one-1, based on the weight of the free radical-polymerizable material.

The following examples are given to illustrate the invention and are not intended as a limitation thereof. Unless otherwise specified, quantities mentioned are quantities byweight.

EXAMPLE I Control Charge a solution of 2 parts of sodium stearate in 150 parts of water to a suitable reaction vessel and heat to 95-100 C. with agitation. Continuously add a mixture of 80 parts of styrene [and 20 parts of acrylonitrile to the heated, agitated soap solution over a period of 2 hours. During the addition of the monomer mixture, continuously add a separate charge consisting of a solution of 0.25 part of potassium pers-ulfate in 50 parts of water. After completing the addition of the monomer and catalyst charges, strip the emulsion of unreacted monomers, coagulate, and dry. The polymeric product has a specific viscosity of 0.180 (measured [as a solution of 0.1% of the polymer in dimethylformamide) and a Rossi-Peakes flow of 0.3 in./2 min. at 135 C. and 1500 EXAMPLE II Repeat Example I except for adding 2 parts of 3,5- dimethylcyclohexen-2-one-1 together with the monomer charge. The product has a specific viscosity of 0.141 (measured as a solution of 0.1% of the polymer in dimethylformarnide) and a Rossi-Peakes flow of 0.6 in./2 min. at 135 C. and l500p.s.i.

As demonstrated above, the addition of 2 parts of 3,5- dimethylcyclohexen-2-one-1 to parts of the monomer charge in the emulsion copolymerization of styrene and acrylonitrile results in decreasing the molecular weight and improving the processability of the product. Similar results are observed when 0.05-5 parts of 3,5-dimethylcyclohexen-Z-one-l are added to 100 parts of the monomer charge in:

1) The suspension polymerization of vinyl chloride at 50 C.,

(2) The mass polymerization of methyl methacrylate at a time-temperature cycle of 5 hours at 80 C. and 3 hours at C.,

(3) The mass C.,

(4) The mass copolymerization of 50 parts of acrylonitrile and 50 parts of dibutyl fumarate at 130 C.,

(5) The suspension copolymerization of 70 parts of styrene and 30 parts of acrylonitrile at a time-temperature cycle of 4 hours at 125 C. and 4 hours at C.,

(6) The emulsion terpolymerization of 60 parts of styrene, 20 parts of acrylonitrile, and 20 parts of dibutyl fumarate at 95100 C., and

(7) The emulsion terpolymerization of 45 parts of styrene, 35 parts of alpha-methylstyrene, and 20 parts of acrylonitrile at 95-100 C.

The larger concentrations of 3,5-dimethylcyclohexen- 2-one-l cause the greater reductions in molecular weight and the greater improvements in the processability of the products.

The invention is a method of regulating the molecular weights of polymers prepared from a free radical-polymerizable material including a polar monomer without employing an organic diluent. The molecular weight regulation is achieved by conducting the polymerization of the free radical-polymerizable material in the presence of a minor amount of 3,5-dimethylcyclohexen-2-one-l.

The amountof molecular weight regulator employed in the practice of the invention is in the range of 0.05- 5%, usually 0.1-3%, based on the weight of the free radical-polymerizable material. 3,5-dimethylcyclohexen- 2-one-l is ineffective as a molecular weight regulator at concentrations lower than 0.05%. Concentrations higher than 5% are usually undesirable, either because the higher concentration causes too great a reduction of the molecular weight of the polymer or because the amount of molecular weight regulator which becomes chemicallycombined into the polymer is largeenough to noticeably affect polymer properties other than the properties attributable to molecular weight. A particular advantage of the molecular weight regulator of the invention is its ability to act as a molecular weight regulator at such low concentrations that substantially its only contribution to the properties of the polymers prepared in its presence is an improvement in processability.

The free radical-polymerizable materials which are polymerized in the presence of the molecular weight polymerization of acrylonitrile at regulator of the invention are materials including a polar monomer, i.e., a monomer which has a dipole moment of at least 1.0 Debye unit. Particularly suitable materials are:

(1) Polar vinylidene monomers, such as acrylonitrile, methacrylonitrile, vinyl chloride, an alkyl a'crylate (e.g., methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethyl hexyl acrylate, dodecyl acrylate, etc.), an alkyl methacrylate (e.g., methyl methacrylate, butyl methacrylate, etc.), and mixtures thereof.

(2) Mixtures of such polar vinylidene monomers with one or more copolymerizable polar or non-polar monomers, such as dialkyl maleates (e.g., dibutyl maleate), dialkyl fumarates (e.g., dibutyl fumarate), acrylic acid, methacrylic acid, conjugated dienes (e.g., butadiene), monovinylidene aromatic hydrocarbons (e.g., styrene, alpha-methylstyrene, alpha-ethylstyrene, m-, and pmethylstyrenes, 0-, m-, and p-methyl-alpha-methylstyrenes, p-isopropylstyrene, andibutylstyrenes, vinyl naphthalene, etc.), and

(3) Mixtures of non-polar vinylidene monomers (e.g., the aforementioned conjugated dienes and monovinylidene aromatic hydrocarbons, etc.) with one or more copolymerizable polar compounds other than the polar monomers mentioned in (1) above, e.g., the monoor dialkyl maleates or fumarates such as the monoor dibutyl ma-leates or fumarates, etc., maleic anhydride, acrylic acid, methacrylic acid, etc.

A polar monomer should comprise at least of the weight of the free radical-polymerizable material. According to one of the preferred embodiments of the invention, the free radical-poly1neriza ble material consists of l090% by weight of acrylonitrile and 90-10% by weight of one or more monovinylidene aromatic hydrocarbons.

The polymerization of the free radical-polymerizable material in the presence of the molecular weight regulator of the invention may be accomplished by any of the mass, suspension, or emulsion polymerization techniques conventionally employed for the polymerization of such materials, usually at temperatures in the range of 30 200 C. at atmospheric or superatmospheric pressure. The reaction mixture should contain a free radical polymerization initiator, such as a peroxy or azo compound, and any ingredient required by the particular polymerization technique employed, e.g., water, an emulsifying agent, a suspending agent, etc. Optional ingredients, such as antioxidants, plasticizers, etc., can also be included in the reaction mixture if desired.

A preferred embodiment of the invention is the use of the molecular weight regulator in polymerization re actions which are conducted in an aqueous medium. Ordinarily in such reactions the weight ratio of water to free radical-polymerizable material is in the range of 9:1 to 2:3. The emulsifying agent, when employed, can be of the anionic, cationic, or nonionic type; the suspending agent, when employed, can be inorganic or organic.

It is within the scope of the invention to conduct the polymerization in the presence of a preformed polymer, e.g., polybutadiene, a rubbery ibutadiene-styrene copolymer or the like, to graft polymeric chains of the free radical-polymerizable material onto the preformed polymer backbone. The molecular weight regulator serves to shorten the chains grafted onto the polymer backbone as well as to lower the molecular weight of any coformed, ungra-fted polymer of the free radical-polymerizable material.

The products of the invention are polymers which contain a minor amount of chemically-combinedmolecular weight regulator and have lower molecular weights then the corresponding polymers prepared in the absence of the molecular weight regulator. Because of their lower molecular weights, they are more easily processable and can be processed, e.g., extruded, molded, etc., in conventional processing equipment Without requiring the use of extreme temperatures which would have a detrimental effect on the strength and color of the products.

The invention is particularly advantageous in that it accomplishes molecular weight regulation without the aid of organic diluents, malodorous mercaptans, or reactive materials which would have to be used in such large amounts as to have a noticeable effect on other polymer properties as well as on processability.

It is abvious that many variations can be made in the products and processes set forth above without departing from the spirit and scope of this invention.

What is claimed is:

1. In a process for polymerizing a free radical-polymerizable material of the group consisting of (a) a polar vinylidene monomer of the group consisting of acrylo nitrile, methacrylonitrile, vinyl chloride, an alkyl acrylate, an alkyl methacrylate, and mixtures thereof, (b) mixtures of said polar vinylidene monomer with a copolymerizable monomer of the group consisting of a dialkyl maleate, a dialkyl fumarate, acrylic acid, methacrylic acid, a conjugated diene, a monovinylidene aromatic hydrocarbon, and mixtures thereof, and (c) mixtures of a non-polar vinylidene monomer with a copolymerizable polar monomer of the group consisting of a monoalkyl maleate, a monoalkyl fumarate, a dialkyl maleate, a dialkyl fumarate, maleic anhydride, acrylic acid, methacrylic acid, and mixtures thereof in the presence of a free radical polymerization initiator, the improvement which comprises conducting the polymerization in the presence of 0.054% of 3,S-dimethylcyclohexen-2-one-l, based on the weight of the free radical-polymerizable material.

2. The process of claim 1 wherein the free radicalpolymerizable material consists of 1090% by weight of a monovinylidene aromatic hydrocarbon and l0% by weight of acrylonitrile.

3. The process of claim 2 wherein the monovinylidene aromatic hydrocarbon is styrene.

4. The process of claim 1 wherein the polymerization is conducted in an aqueous medium.

References Cited by the Examiner Baysal: Journal of Polymer Science, 33 (1958), pages 381-388.

JOSEPH L. SCHOFER, Primary Examiner. H. WONG, Examiner. 

1. IN A PROCESS FOR POLYMERIZING IN FREE RADICAL-POLYMERIZABLE MATERIAL OF THE GROUP CONSISTING OF (A) A POLAR VINYLIDENE MONOMER OF THE GROUP CONSISTING OF ACRYLONITRILE, METHACRYLONITRILE, VINYL CHLORIDE, AN ALKYL ACRYLATE, AN ALKYL METHACRYLATE, AND MIXTURES THEREOF, (B) MIXTURES OF SAID POLAR VINYLIDENE MONOMER WITH A COPOLYMERIZABLE MONOMER OF THE GROUP CONSISTING OF A DIALKYL MALEATE, A DIALKYL FUMARATE, ACRYLIC ACID, METHACRYLIC ACID, A CONJUGATED DIENE, A MONOVINYLIDENE AROMATIC HYDROCARBON, AND MIXTURES THEREOF, AND (C) MIXTURES OF A NON-POLAR VINYLIDENE MONOMER WITH A COPOLYMERIZABLE POLAR MONOMER OF THE GROUP CONSISTING OF MONOALKYL MALEATE, A MONOALKYL FUMARATE, A DIALKYL MALEATE, A DIALKYL FUMARATE, MALEIC ANHYDRIDE, ACRYLIC ACID, METHACRYLIC ACID, AND MIXTURES THEREOF IN THE PRESENCE OF A FREE RADICAL POLYMERIZATION INITIATOR, THE IMPROVEMENT WHICH COMPRISES CONDUCTING THE POLYMERIZATION IN THE PRESENCE OF 0.05% OF 3,5-DIMETHYLCHCLOHEXENE-2-ONE-1, BASED ON THE WEIGHT OF THE FREE RADICAL-POLYMERIZABLE MATERIAL. 